A representative OFDMA wireless system is the IEEE 802.16d/e system standardized by the IEEE 802.16 standardization group. The IEEE 802.16d/e system employs a wide data transmission bandwidth and adopts an OFDMA scheme which allows users to share resources in an efficient manner. In the IEEE 802.16d/e system, a basestation allocates uplink and downlink resources to terminals wirelessly connected thereto for each frame. Accordingly, the basestation needs to broadcast the location and size of the uplink and downlink resources allocated to each terminal via uplink and downlink maps placed at the head of each downlink subframe.
FIG. 1 illustrates an exemplary frame structure of the IEEE 802.16d/e system. Referring to FIG. 1, a frame is a combination of resources on time and frequency axes. The vertical axis represents the subchannels constituting a system bandwidth, which may be identified by subchannel logical numbers s to s+L, and, the horizontal axis represents the time, which may be identified by OFDMA symbol numbers k to k+46. The frame includes a DL (downlink) subframe and a UL (uplink) subframe. Further, a TTG (transmit/receive transition gap) is inserted after the DL subframe and an RTG (receive/transmit transition gap) is inserted after the UL subframe, thereby preventing interference between uplink and downlink transmissions.
The DL subframe includes a preamble indicating the start of a frame; broadcasting information such as FCH (Frame Control Header), DL-MAP (downlink map) and UL-MAP (uplink map); and DL (downlink) bursts for use in data transmission from a basestation to terminals.
The UL subframe includes control channels such as a ranging channel for use in the bandwidth requests of terminals, an ACK (acknowledgement) channel for informing the basestation whether the terminals correctly receive data and a CQI (Channel Quality Indicator) channel for informing the basestation of channel status of the terminals; and UL (uplink) bursts for use in data transmission from the terminals to the basestation.
The DL-MAP and the UL-MAP in the DL subframe include a DL-MAP_IE (downlink map information element) and a UL-MAP_IE (uplink map information element), respectively. The DL-MAP_IE and the UL_MAP_IE contain therein resource allocation information, i.e., locations and sizes of the bursts, and destination information of the DL and UL bursts, respectively. Hence, each terminal can check whether the DL and UL bursts are allocated to itself by using the DL-MAP_IE and the UL-MAP_IE, and can transmit/receive data via the allocated resource.
As described above, since the resource allocation information is broadcast to all active terminals for each frame, the resources of the IEEE 802.16d/e system can be flexibly allocated according to the amount of data transmitted/received to/from the terminals. However, if the amount of data transmitted/received to/from each terminal is small and thus the data from/to a large number of terminals are multiplexed within one frame, the size of the DL-MAP and UL-MAP containing therein the resource allocation information for a large number of multiplexed terminals becomes larger, which results in excessive overhead in the system. In particular, in case of persistent services with light traffic, e.g., voice call services or video conference services, as the number of terminals connected to a basestation increases, the resource allocation information significantly increases in proportion to the number of the connected terminals, which may significantly degrade the system performance.